Human Nutrition

Thermic effect of food

Human Nutrition 3(3+0)

Lesson 8 : Physical Activity and Thermogenic Effect of Food

Thermic effect of food

Thermogenesis literally means heat generation. All the energy substrates in the metabolic reactions in the body are eventually degraded into heat. However, in energy metabolism, thermogenesis is defined as an increase in metabolic rate that occurs in response to a stimulus such as exercise, food ingestion or exposure to cold. The consequent increase in metabolism finally results in generation of heat. Diet-induced thermogenesis (DIT) leads to only a small increase in metabolism, of about 10%. Cold or exercise-induced increase in metabolic rate however can be much higher. Energy expended due to increased metabolic rate during thermogenesis is not available for useful work but mostly dissipated as heat. Thermogenesis is also invoked by the body for disposing off extra energy ingested and is believed to play a role in promoting or preventing obesity.

In addition to basal metabolism and physical activity, the body uses energy to digest, absorb, and further process food nutrients. Energy used for these tasks constitutes the thermic effect of food. The energy cost of this thermic effect is analogous to a sales tax. It is like being taxed about 5% to 10% for the total Kcalories we eat. The charge covers the cost of processing those Kcalories. To supply the body with 100 kcalories for basal metabolism and physical activity, a person must then eat between 105 and 110 kcalories. The processes of digestion, absorption, and metabolism use extra 5 to 10 kcalories to modify the energy-yielding nutrients for use. Given a daily kcalorie intake of 3000, the thermic effect of food would use 180 to 300 kcalories. The total amount used varies little between individuals.

Thermic Effect of FoodThe increase in metabolism occurring during the digestion, absorption, and metabolism of energy-yielding nutrients. This represents 5% to 10% of k calories consumed.